<?php 
   $nomPrenomV = $pdo->getNomPrenomVisiteur();
?>
<form method="POST" action="index.php?uc=validerFrais&action=validerFrais"> 
                    <select name="id" size="1">
<?php
foreach ($nomPrenomV as $data) {
    echo '<option value="' . $data['id'] . '">';
    echo $data['nom'] . " " . $data['prenom'];
}
echo '</select>';

echo '<select name="annee" size="1">';
getDernierMois();

echo '</select><input type="submit" value="Envoyer"></form>';

$pdo->getLesInfosFicheFrais($_POST['id'], $_POST['annee']);